The present invention relates to heavy duty electrical plugs and receptacles; more particularly, the invention relates to a system for mating plugs to receptacles, through the use of indexers and polarizers which fit within the plug and receptacle, to create a system of mated plugs and receptacles and thus ensure that a specific plug can only be mated to a receptacle having the same electrical rating.
Heavy duty electrical plugs, like those addressed by the invention, are disposed on high voltage cables and are connected to a receptacle to energize portable electrical equipment like portable welders. Each plug is equipped with a certain number of female conductors which are inserted into a corresponding number of mating male conductors in a receptacle. Typically, a receptacle of a specific electrical rating will be installed in a location as a need for equipment requiring that rating arises. The physical size of the plug and receptacle varies with amperage ratings of 30, 60 and 100 amps. A heavy duty plug arrangement of this type is disclosed in U.S. Pat. Nos. 5,167,527 and 5,135,404 assigned to the same entity as the present invention and those documents are incorporated by reference herein.
Within each amperage rating, numerous voltages and phases are possible for different plugs having the same number of conductors. For example, a 30 amp plug having three female conductors could be wired for a 120 V-single phase, 240 V-single phase, 480 V-single phase or 600 V-three phase use, by varying the voltage potential on each of the conductors. For example, a 120 V PG,3 single phase configuration would have one conductor of 120 V potential, one conductor at 0 V potential, and one at ground potential. In the three-phase configuration, each conductor is energized to an equal, but 120.degree. out of phase, voltage. Because a plug or receptacle with any of the foregoing voltage arrangements uses the same number of conductors, they appear identical to the user. However, insertion of a plug having one electrical rating into a receptacle having a different rating, can cause catastrophic results such as severe injury, loss of life or the destruction of expensive equipment.
Over the past 50 years, users of these plugs and receptacles have become accustomed to determining the rating of a plug by the rotational attitude of the conductors in relation to the location of identifying splines or notches on the plug and receptacle. Presently there are a number of schemes whereby conductors of a heavy duty plug are polarized or fixed at a certain rotational angle within the plug body to fit a receptacle having similarly polarized conductors to reduce the potential of components being mismatched to voltage supplies. In one such arrangement, different sets of matching plugs and receptacles are constructed with the conductors permanently polarized depending upon the electrical rating thereof and then labeled. The obvious disadvantage to this arrangement is that the parts of the plugs are not interchangeable and the industrial distributor must keep plugs and receptacles on hand for each possible wiring arrangement.
In another type of prior art arrangement, mating male and female conductor assemblies for different electrical ratings are available for use with a standard plug body whereby the polarization of the conductors in the plug is determined by the conductor assembly chosen. The conductor assembly in the receptacle is likewise interchangeable to provide a matching polarization for receiving the plug. However, those plugs and receptacles require different conductor assemblies for each different wiring possibility, which still results in a large inventory for the electrical distributor.
There is a need, therefore, for a plug and receptacle system using one set or type of conductors and parts whereby the conductors of the plug and conductors of the receptacle can be arranged or indexed in a certain configuration to guarantee that a plug wired for one electrical rating is not mated with a receptacle wired for a different electrical rating.
There is a further need for a heavy duty plug and receptacle, each of which can be arranged with conductors of a certain polarization without the need for changing a major part of the plug or receptacle.
There is yet a further need for a heavy duty plug and receptacle system in which the rotational attitude and the electrical rating of the conductors can be easily visually determined with minimal inspection of the plug or receptacle.